Mercury vapor rectifier



Jan. 5, 1937. R. M. HEINTz MERCURY VAPOR RECTlFIER Filed April 25, 1952 Patented Jan. r5, "1937 PATENT OFFICE MERCURY VAPOR RECTIFIER Ralph M. Heintz, Palo Alto, Calif., assignor to Heintz & Kaufman,

Ltd.,

San Francisco, Calif.,

a corporation of Nevada Application April 25, 1932, Serial No. 607,297

3 Claims.

My invention relates to the rectication of alternating currents and more specifically to a mercury vapor rectifier of the hot cathode type wherein the vapor pressure of mercury is regulated independently of the load carried by the rectifier.` I Y Among the objectsfof my invention are: To provide a mercury vapor rectifier in which the z vapor pressure cf mercury may be regulated; to

provide a rectier which will operate at the most efficient vapor pressure regardless of load; to provide a small, compact rectifier which will handle largev amounts of power; and to provide a method of regulating the vapor pressure of mercury in a rectier of the hot cathode type..

n l. Other objects of my invention will be appar- `ent or will be specifically pointed out in the description forming a part of this specification, but Ido not. limit myself to the embodiment of my invention herein described, as various forms `may be adopted within the scope of the claims.

. Referring to the drawing:

' Figure 1 Ais a longitudinal sectional view of a rectifier embodying my invention. n

, Figure 2 is a cross section view taken at a plane indicated by line 2--2 in Figure 1. Y

Figure 3 is a longitudinal elevation partly in section, of a modification of my device, drawn to a smaller scale.

It is a well known fact that the vapor pressure of mercury is dependent on temperature. At 25 C. the pressure is .002 mm., at 140 C. `the Vapor pressure is 1.85 mm. mercury. With an increase of 100 C. the pressure rises to 59 mm, mercury andrwith an increase of 200 the pressure ascends to 548 mm. of mercury. Devices such as a mercury arc rectifier, in which mercury vapor is used as an ionization medium, are always subjectto changes in internal vapor pressure during operation, and provision must be made to regulate these changes.

Normal, or initial pressure, is dependent on the temperature of the surroundings. Changes of temperature during operation are dependent upon the ratio of heat generation to heat radiation in rectiliers as commonly constructed. Hence, in the operation of prior vapor devices having given physical dimensions and electrical characteristics of construction, the density of vapor has heretofore been controlled by regulation of current flow and by variation of the size of the envelopes.

Mercury Vapor rectiiiers are classiiied into two groups, one.l group comprises the low pressure types, in which high voltages are used, and are (Cl. .Z50-27.5)

characterized by operation at a pressure of from 4 1 to 50 microns of mercury. .In this type the amount of current in the tube is solely dependent upon the electron'emission of the cathode, de-ionization time is short, and the rectier has 5 no reverse current. The second group comprises the high pressure types which operate at a pressure of from 1 to 5 cm. mercury. The current is augmented by ionization by collision and large amounts may be passe-d at low voltage. De-ion- 1G ization times are slow and some reverse current is usually present.

The proper operation of either type of rectier depends upon the close regulation of vapor pressure, and heretoforehsuch regulation has been attained by increasing the size of the containers in accordance with increased power. Consequently, mercury Vapor rectii'lers of high power at present are large and unwieldy, and when glass is used for a container, a denite limit of power is reached due to difficulties in the manufacture of large bulbs.

I have found it neither necessary nor desirable to increase the size of the container when using high powers and heavy currents. Investigation has proved that internal vapor pressure may be controlled and regulated by adjusting the temperature of contained mercury in liquid phase in only a small constricted portion of the container. The vapor pressure in the entire rectifier envelope conforms to the vapor pressure which is under regulation in the constricted portion, regardless of heat generated by the load, or dissipation by the portionsl of the container immediately adjacent the electrodes.

Broadly speaking my invention comprises a mercury vapor rectifier having a heated electron-emitting cathode and a cooperating anode, enclosed in a bulb. A portion of this bulb is used 40 as a container for a small amount of mercury in liquid phase, and this portion of the container is provided with cooling means, so that no matter what temperature is generated by the load between anode and cathode, or what the dissipation of heat may be from the portion of the envelope adjacent the electrodes, the temperature of the constricted portion is regulated, and the vapor pressure is thereby kept in the required range.

I also keep the envelope adjacent the electrodes as hot as the glass will conveniently permit so that no mercury in liquid phase can remain on it.

A preferred embodiment of my invention is shown in Figure l. An envelope l preferably of high melting point glass such as pyrex, is provided with a bulbous portion 2 and a restricted portion 4, preferably tubular in section. Sealed to the end of the tubular portion in the customary manner is a reentrant stem 5. On this stem is mounted an electron-emitting cathode 6, preferably of tungsten wire welded to filament leads 1, and sustained in hairpin shape by stay 9. The filament lead wires 'I are sealed into the stem at the pinch I0.

Surrounding the cathode is the anode I I, preferably cylindrical in form and made out of a highly refractory metal such as tungsten or tantalum. The anode is positioned by being welded to plate supports I2, and a plate wire I4 connects with plate lead I5, which is sealed into the glass of the bulb at I6. A cap I'I is provided for contact purposes and the end of the lead is welded or soldered to the cap at I9. The operating structure of the rectifier is preferably located in the center of bulb 2.

The glass structure with its contained electrodes is thoroughly baked out in an oven and the air carefully exhausted in accordance with methods well known in the art. It is advisable to obtain as high a vacuum as possible and it is desirable to burn the filament at full brilliancy and heat the anode to a bright red heat, to remove all traces of occluded gas from the metals. After the exhaust has been completed a few drops of purified mercury 20 are introduced into the envelope in any convenient manner, and the tube should then be operated as a rectiiier while connected to the vacuum pump, gradually increasing the load until the load carried by the device approaches or passes that for which the rectifier is eventually intended. It has been found that it is possible to allow the entire envelope to attain a temperature just below that at which the walls soften. No cooling of the device is desirable at this point. This increase in temperature is a result of the increased voltage drop in the tube which in turn is due to the increase in vaporY pressure of the mercury. The increased voltage drop heats the elements and these in turn heat the envelope. I thereby promote fast internal heating of the device, which combined with oven baking, gives a finished tube in which the mer cury is of extreme purity. After the rectifier has been run at full loads for some time, it is sealed off from the pumps and allowed to cool.

An air cooling structure ZI is provided, preferably made from a metal having good heat conduction such as copper or brass. One end of this structure is constructed to form a base 22, provided with a contact pin 24, which is insulated from the base by a lavite or other heat resisting insulator 25. The other end of the structure is left open and is of such a diameter that the restricted portion 4 of the envelope will lit snugly inside, as shown in Figure 2.

The sides of the structure are provided with longitudinal fins 26 to promote heat dissipation. Variation of the area of the fins offers a convenient method of controlling the heat dissipation, and may be large for the rectifier which requires a low vapor pressure, and smaller for the type which uses higher vapor pressures.

In -a modification of my device as shown in Figure 3, a liquid-cooling jacket 21 is substituted for the longitudinal ns 26. Liquid is circulated through the jacket as indicated by the arrows, and effectively cools the mercury. Cooling may be very accurately regulated by a valve 29 and the temperature of the restricted portion of the envelope kept constant.

The base 22 and the cooling structure may be, if desired, permanently xed in place on the envelope. After the cooling structure has been applied to the envelope, one filament lead is welded to the structure at 30, thev other welded to the contact pin 24 at 3l.

The rectier is thereupon ready for operation. Current is supplied to the filament and a suitable positive voltage applied to the anode. As a room temperature of 20 F. is sufficient to provide a vapor pressure of .0013 mm. mercury, the arc will strike and the heat generated by operation will raise the vapor pressure.

As the load continues, heat generated by the electrodes would ordinarily increase the vapor pressure of the mercury beyond the point at which proper operation of the device is obtained. The cooling of the mercury by the structure surrounding the restricted portion containing the mercury prevents such rise in vapor pressure, as it has been found that the vapor pressure of the entire rectifier is the same as that of the coolest portion.

It follows, therefore, that no matter how much heat is generated by the electrodes in operation, I can control the vapor pressure of the gas immediately surrounding the electrodes within a predetermined range by cooling the mercury at a point removed from the electrodes. This feature has proved to be of great advantage as less current has to be supplied to the iilament due to decreased radiation from the envelope surrounding the electrodes, and the overall size of the tube can be greatly reduced.

I construct the cooling structure of such area that at ordinary room temperatures the temperature of the mercury in the high pressure type may be maintained between 180 C. and 200 C. when full loads are carried by the rectifier. At these loads the rectifier structure and surrounding envelope is operating at a temperature 'far above that which could be allowed in previous devices of this type, and no mercury in liquid phase can condense upon it.

In the low pressure type the mercury is further cooled to between 25-60 C., either by increasing the area of the air cooling Iins, or by Water cooling the constriction, as described.

With either type the vapor pressure may be accurately regulated within the elicient operating range of pressures desired.

I claim:

1. A rectifier comprising the combination' of an envelope having an expanded portion and a restricted portion, an incandescible cathode and' an anode in said expanded portion, mercury in liquid phase in said restricted portion only, and means for cooling the mercury in said restricted' portion only to control the vapor pressure in the entire envelope independently of the heat generated by said cathode and anode.

2. A rectifier comprising the combination of an envelope having an expanded portion and an elongated restricted portion having a reentrant stem therein, an incandescible cathode and an anode mounted on said stem and positioned within said expanded portion, mercury in liquid phase in said restricted portion only and disposed around said stem, and means for cooling the mercury in said restricted portion only to control the vapor pressure in the entire envelope independently of the heat generated by said cathode and anode. Y

3. A rectifier Cil comprising thecombination of K,

an envelope having an expanded portion and a restricted portion, an incandescible cathode and an anode in said expanded portion, mercury in liquid phase in said restricted portion only, and a base fixed to the terminus of said restricted portion whereby said envelope may be mounted in upright position with the terminus of said restricted portion lower than the remainder of the envelope, said base being prolonged to form means for cooling the mercury in said restricted portion only to control the vapor pressure in the entire envelope independently of the heat gen- 5- erated by said cathode and anode.

RALPH M. HEINTZ. 

